A known device for extracorporeal blood treatment comprises at least a treatment unit such as, for example, a dialyzer and/or a dialyzer device, or a filter, ultrafilter or plasma filter of a different filter unit with a semipermeable membrane which separates the treatment unit into two chambers. An extracorporeal blood circulation permits a flow of blood taken from a patient through the first chamber and back to the patient. At the same time, a dialysis fluid (treatment fluid) flows in the opposite direction through an appropriately designed circulation via the second chamber.
The known device comprises moreover an infusion line for a substitution fluid, a fluid inlet line connected with the second chamber on the inlet side, and a fluid outlet line connected with the second chamber on the outlet side. Moreover, sensors are provided for determining a first parameter relating to the blood volume of a patient, a second parameter relating to a ultrafiltration flow rate or a weight loss rate of the patient, a third parameter relating to a conductivity or concentration of a fluid flowing through the fluid line and/or the infusion line, and a fourth parameter relating to a infusion flow rate. A control unit carries out a control procedure for compensating a fluctuation of the blood volume and an adjusting sequence for applying a transmembrane pressure with values for maximising the convective exchange processes.
In the known device the transmembrane pressure and the blood flow are correlated, and depending on the speed of the blood flow and its changes different functions are carried out, for example, a new operating mode is started or an operating mode is stopped.
In renal replacement therapies with devices of the known type various complications can occur. For example, devices are designed to be able to intervene, if a calculable (excessive) worsening of the therapy result could occur in the case of a parameter intervention by the user which had not been optimally adjusted.
For example, when starting the therapy, i.e. at a time when already all therapy parameters and the form of therapy have been selected, one can try to achieve as fast as possible also a predetermined blood flow in order to start therapy. If this is not immediately successful, and therapy starts with a lower blood flow, a hemoconcentration of the blood in the dialyzer may occur. This is presently systematically monitored but treatment as such is permitted by indicating, for example, an exceeding of the ultrafiltration/cross rate wherein due to existing limit values (30% at a therapeutically aimed at maximum value of 25%) only a small margin exists. Another case occurs in therapy, if due to a problematic access the blood flow needs to be reduced even if only temporarily. The user is not allowed to reduce and/or change the prescribed substitution quantity or type of therapy (for example from post-dilution to pre-dilution) without consultation with the physician.
Moreover, presently known assemblies do not take into account the forming of a secondary membrane during the first minutes. Complications in a renal replacement therapy also result in a clotting in the extracorporeal circulation, for example, due to a too low heparin dosing, a too low flow and too high filtration rates which regularly manifests itself by an increase of the filter inlet pressure. By this, proteins can deposit on the filter inside and result in a decrease of the filtration performance. Due to the deposit, the secondary membrane is formed, which would have to be tackled by the user by a sufficient heparinization, a pre-dilution or the increase of the substitute, and by decrease of the filtration (decline of the screening coefficient) in the case of formation of secondary membranes a reduction of the filtration pressure Pf and thus an increase of the transmembrane pressure TMP results.
Since the precise mechanisms of occurrence of the secondary membranes are not yet fully known, and moreover measures influencing them are possible only in a limited way in hemofiltration due to the risk of hemolysis, here as well a consultation with the physician in each case is required, or, as mentioned above, the secondary membrane formation is adversely unconsidered in known assemblies. Nor are any processes carried out automatically which evaluate the cross-flow rate and/or cross rate and prevent an application error. Hence, the user must immediately interpret correctly all consequences from a warning message of the device or system but nevertheless can decide only for two sub-optimal approaches. On the one hand, he or she can interrupt therapy until the blood flow is adequate again. But the end of treatment is also delayed automatically as a result. On the other hand, he or she can accept the membrane load and the associated reduction in effectiveness and subsequently a reduced therapy result.